Versatile Papertronics: Photo‐induced Synapse and Security Applications on Papers

Paper is a readily available material in nature. Its recyclability, eco‐friendliness, portability, flexibility, and affordability make it a favored substrate for researchers seeking cost‐effective solutions. Electronic devices based on solution process are fabricated on paper and banknotes using PVK and SnO 2 nanoparticles. The devices manufactured on paper substrates exhibit photosynaptic behavior under ultraviolet pulse illumination, stemming from numerous interactions on the surface of the SnO 2 nanoparticles. A light‐modulated artificial synapse device is realized on a paper at a low voltage bias of −0.01 V, with an average recognition rate of 91.7% based on the Yale Face Database. As a security device on a banknote, 400 devices in a 20 × 20 array configuration exhibited random electrical characteristics owing to the local morphology of the SnO 2 nanoparticles and differences in the depletion layer width at the SnO 2 /PVK interface. The security Physically Unclonable Functions (PUF) key based on the current distribution extracted at −1 V show unpredictable reproducibility with 50% uniformity, 48.7% inter‐Hamming distance, and 50.1% bit‐aliasing rates. Moreover, the device maintained its properties for more than 210 days under a curvature radius of 8.75 mm and bias and UV irradiation stress conditions.